Implantable medical devices (IMDs) can perform a variety of diagnostic or therapeutic functions. An IMD can include one or more cardiac function management features, such as to monitor the heart or to provide electrical stimulation to a heart or to the nervous system, such as to diagnose or treat a subject, such as one or more electrical or mechanical abnormalities of the heart. Examples of IMDs can include pacemakers, automatic implantable cardioverter-defibrillators (ICDs), cardiac resynchronization therapy (CRT) devices, implantable monitors, neuromodulation devices (e.g., deep brain stimulators, or other neural stimulators), cochlear implants, or drug pumps, among others. IMDs can include a telemetry circuit and an antenna, coupled to the telemetry circuit, such as to provide magnetic coupling between the IMD and one or more other devices to provide wireless communication (e.g., to send information, such as physiological or other information, from the implantable medical device to the external device, or to receive information, such as programming instructions, at the implantable medical device from the external device).
Magnetic coupling can be used to provide short-range (e.g., centimeters) communication between an implantable medical device implanted in a body and an external device, or between an implantable medical device outside of the body and an external device. Magnetic coupling communication largely relies on near-field coupling, where the field distribution is highly dependent upon the distance between and relative orientations of the transmitting and receiving antennas. This limits the effective range of wireless communication between the implantable medical device and the external device.